The excitonic insulator (EI) phase is a state of matter that was first proposed more than 50 years ago [numbers[1]}, [2]}, [3]}]. It was theorized that below a critical temperature (T\(_c\) ), weakly screened Coulomb interactions in small bandgap semiconductors and semimetals could lead to the formation of an exciton condensate in the ground state (Fig. REF A). In the proposed theoretical framework, condensation would result from the spontaneous breaking of a U(1) continuous symmetry, which describes the separate conservation of charges in the valence and conduction bands. Therefore, this macroscopic state would be accompanied by characteristic collective excitations, including an amplitude (Higgs) mode and a gapless phase (Goldstone) mode, as is the case for other correlated systems, like superconductors. The emergence of the latter collective mode would lead to intriguing quantum phenomena such as superfluidic transport [numbers[4]}, [5]}].
